One of the most common areas where de-icing of frozen surfaces required in northern climates is that of de-icing aircraft and helicopter blades. The most common method of de-icing these vehicles is by spraying wings, fuselage and blades with a hot glycol water solution. The main function of the glycol spray is to melt the ice and the snow already there and to warm the surface in order to provide a brief period of protection against further icing. Many other hot liquid solutions, organic and inorganic, have been described in patents and have been shown to work but they all have major drawbacks and glycol remains the material of choice. De-icing a large aircraft can cost upwards of $10,000, and it is estimated that Glycol sales to the airline industry exceed $200 million per year. Infrared heating systems are also available for aircraft de-icing and have found some limited applications. Helicopter blades present a special problem as it is considered desirable to avoid getting organic or inorganic material, even glycol in the blade mechanisms. Various systems are described to de-ice helicopter blades using warm air. These usually involve the use of a sock or other form of cover over the blades through which warm air is circulated.
In Canada and other northern regions, there is a need to thaw the ground in construction, municipal works and other activities as concrete cannot properly be laid over frozen ground. Now that construction is a year round activity, builders are increasingly making use of ground thawing techniques. Two approaches to ground thawing are commonly used. In the first, the space over the area to be thawed is covered and warm air is introduced into the space. In a second method, an array of flexible hose is laid over the area to be thawed and covered with an insulating blanket. Hot water or glycol is then circulated through the hose. Both methods are slow. Dry, warm air does not contain a lot of heat unless introduced at very high temperatures; something that is not practiced in most applications. In the second method, higher temperatures can be used but only a small fraction of the ground surface comes in contact with the hot hoses. Heat transfer is limited by the rate of transfer to the ground. Both methods being relatively ineffective, the ground thawing process can hold up large construction projects for numbers of days or weeks at a very high cost. Thus, there appears to be a need for a less costly method of de-icing of aircraft and helicopter blades and a faster, more effective method for thawing ground around construction sites.